Development and sensitivity analysis of a model for assessing stratification and safety of Lake Nyos during artificial degassing
Development and sensitivity analysis of a model for assessing stratification and safety of Lake Nyos during artificial degassing
复制标题
尼奥斯湖人工脱气期间分层和安全评估模型的开发和敏感性分析
DOI：
10.1007/s10236-003-0032-0
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发表时间：
2003
期刊：
影响因子：
2.3
通讯作者：
G. Tanyileke
中科院分区：
文献类型：
--
作者：
M. Schmid;A. Lorke;A. Wüest;M. Halbwachs;G. Tanyileke
为了防止尼奥斯湖灾难性的二氧化碳喷发再次发生，该湖已经制定了一项脱气计划。由于担心湖泊的脱气会降低密度分层的稳定性，因此迫切需要一种模拟工具来预测不同情景下湖泊分层的演变。本文介绍了一个用于预测尼奥斯湖CO2和溶解固体浓度、温度结构和水柱稳定性的数值模型的发展。用1986年至1996年的二氧化碳浓度和温度曲线对该模型进行了检验。它很好地再现了在湖中观察到的一般混合模式。然而，混合的强度往往是过高估计的，而在单分子分子低估。由于k-epsilon模型的参数化，或者由于地表热通量计算的不确定性，造成了对混合深度的过高估计。模拟的混合深度对地表热通量高度敏感，混合深度误差在一年到一年之间传播。因此，对混合离子加深的精确模拟要求在气象强迫和热通量的参数化方面具有很高的精度。气象资料和计算热通量的公式都没有达到必要的精度。因此，为了获得安全脱气的鲁棒边界条件，在安全性分析中考虑不同的强迫情景是必不可少的。1986 ~ 1996年湖底温度和CO2输入可以很好地模拟，湖底温度输入为18 l s−1，CO2浓度为0.395 mol l−1，温度为26℃。本研究结果表明，该模型在用于预测尼奥斯湖脱气过程中的稳定性和安全性之前，需要使用更详细的现场数据进行校准。
To prevent the recurrence of a disastrous eruption of carbon dioxide (CO2) from Lake Nyos, a degassing plan has been set up for the lake. Since there are concerns that the degassing of the lake may reduce the stability of the density stratification, there is an urgent need for a simulation tool to predict the evolution of the lake stratification in different scenarios. This paper describes the development of a numerical model to predict the CO2 and dissolved solids concentrations, and the temperature structure as well as the stability of the water column of Lake Nyos. The model is tested with profiles of CO2 concentrations and temperature taken in the years 1986 to 1996. It reproduces well the general mixing patterns observed in the lake. However, the intensity of the mixing tends to be overestimated in the epilimnion and underestimated in the monimolimnion. The overestimation of the mixing depth in the epilimnion is caused either by the parameterization of the k-epsilon model, or by the uncertainty in the calculation of the surface heat fluxes. The simulated mixing depth is highly sensitive to the surface heat fluxes, and errors in the mixing depth propagate from one year to the following. A precise simulation of the mixolimnion deepening therefore requires high accuracy in the meteorological forcing and the parameterization of the heat fluxes. Neither the meteorological data nor the formulae for the calculation of the heat fluxes are available with the necessary precision. Consequently, it will be indispensable to consider different forcing scenarios in the safety analysis in order to obtain robust boundary conditions for safe degassing. The input of temperature and CO2 to the lake bottom can be adequately simulated for the years 1986 to 1996 with a constant sublacustrine source of 18 l s−1 with a CO2 concentration of 0.395 mol l−1 and a temperature of 26 °C. The results of this study indicate that the model needs to be calibrated with more detailed field data before using it for its final purpose: the prediction of the stability and the safety of Lake Nyos during the degassing process.